1. Field of the Invention
The present invention relates to a speaker apparatus for converting an electrical signal into an acoustic signal, and more specifically, toastructure for improving the soundquality.
2. Description of the Related Art
Conventionally, acoustic reproduction is performed by a speaker system 1 having a basic structure as shown in FIG. 7. In the speaker system 1, one or a plurality of speaker units 2 are accommodated in an enclosure 3. The speaker unit 2, which in many cases assumes a generally conical cross-section, has a vibration plate 4 called xe2x80x9ccone.xe2x80x9d The speaker unit 2 is also equipped with a magnetic circuit 5, which has a main magnet 6, a center pole 7, and a plate 8. In a magnetic gap between the center pole 7 and the plate 8 is concentrated magnetic flux generated by the main magnet 6 in high density. A voice coil 9 whose tip is joined to the basal portion of the vibration plate 4 is suspended in the magnetic gap.
When the voice coil 9 is energized, driving force acts on the voice coil 9 in the magnetic gap and the vibration plate 4 is thereby displaced, whereby sound waves are emitted from the vibration plate 4 to the neighboring air. Each speaker unit 2 is accommodated in the enclosure 3 to prevent back-side sound waves (opposite in phase to front-side sound waves) from going around the speaker unit 2 to the front side. Each speaker unit 2 has a frame 10 for use in fixing of the magnetic circuit 5 and for vibratably supporting the vibration plate 4. The frame 10 is fixed to the enclosure 3.
Having a structure called xe2x80x9cexternal magnet type,xe2x80x9d the magnetic circuit 5 is suitable for a case where a ferrite magnet is used as the main magnet 6. However, the external magnet type magnetic circuit 5 leaks a large amount of flux to the outside. Where it is used together with a cathode-ray tune (CRT) for acoustic reproduction as part of an audio-visual apparatus such as a TV receiver or a video player or acoustic reproduction for a personal computer or a game machine, there is fear that a color purity error or a distortion may occur and lower the image quality. Countermeasures for decreasing the leakage magnetic flux include attaching a cancellation magnet to the rear side of the magnetic circuit 5 and, in addition, covering the magnetic 11 circuit 5 with a shield cover 12.
The electromagnetic driving force acting on the voice coil 9 is transmitted to the neighboring air from the vibration plate 4. The vibration force 4 applies pressure to the neighboring air and receives reactive force therefrom. The reactive force that the vibration plate 4 receives is transmitted to the magnetic circuit 5 through electromagnetic interaction between the voice coil 9 and the magnetic circuit 5 and then transmitted from the magnetic circuit 5 to the enclosure 3 via the frame 10. Therefore, in the speaker system 1, when sound is outputted from the vibration plate 4 by driving each speaker unit 2 electrically, the speaker unit 2 itself vibrates and this vibration is transmitted to the enclosure 3. Sound is also emitted from the surfaces of the enclosure 3. Being opposite in phase to the sound emitted from the vibration plate 4, this sound interferes with the sound emitted from the vibration plate 4. As such, this sound is a factor of deteriorating the quality of sound emitted from the speaker system 1 as a whole. Further, because of reaction to the movement of the vibration plate 4 for emitting sound, the center pole 7 side of the magnetic circuit 4 tends to vibrate. Therefore, the efficiency of energy transmission from the vibration plate 4 to the air is low, which influences the transient characteristic of sound and, in terms of the sound quality, lowers a sense of speed to be given to a listener.
Japanese Unexamined Patent Publications JP-A 5-153680 (1993), JP-A11-146471 (1999), etc. disclose a technique in which in the enclosure each speaker unit is not fixed to the front side of the frame of the speaker unit but to the rear side of the magnetic circuit. By fixing the magnetic circuit to a grounding surface to make vibration hard to be transmitted to the magnetic circuit and to be transmitted from the frame to the enclosure, it is expected that the degree of sound emission from the enclosure will be lowered and the deterioration of sound quality will be decreased.
To strongly support the magnetic circuit portion while accommodating each speaker unit in the enclosure as in the above prior art technique, it is necessary to, for example, make the enclosure of a dividable type and assemble the enclosure after completion of support of each speaker unit. This results in problems that the number of assembling steps of the speaker apparatus increases and the structure of the enclosure becomes complex. There may be cases where the enclosure cannot be divided as exemplified by a speaker that is attached to a vehicle door as the enclosure.
An object of the invention is to provide a speaker apparatus in which a speaker unit itself can suppress vibration that is caused by reaction to the movement of a vibration plate and which can provide sound quality with a good transient characteristic even in a state that the speaker apparatus is attached to an enclosure.
A first aspect of the invention provides a speaker apparatus comprising a speaker unit including a converter, having a magnetic circuit, for converting an electrical signal into mechanical vibration along an axial line direction of a voice coil, a vibration plate for emitting sound waves to a front side of the converter, and a frame fixed to the converter, for vibratably supporting the vibration plate from its rear side; and a weight heavier than the speaker unit, having a boss formed so as to project to a front side from a central portion of the weight along the axial line of the voice coil, a cross section of the boss taken perpendicularly to the axial line being smaller than that of the magnetic circuit, a tip of the boss being fixed to a rear side of the magnetic circuit.
This speaker apparatus that converts an electrical signal into an acoustic signal and emits the latter to the front side has the speaker unit and the weight. The speaker unit has the converter for converting an electrical signal into mechanical vibration, the vibration plate provided on the front side of the converter, for emitting sound waves, and the frame that is fixed to the converter and vibratably supports the vibration plate from the rear side. Mechanical vibration that is produced from an electrical signal is emitted, as sound waves, from the vibration plate to the neighboring air. Reactive force that acts on the vibration plate from the air is returned to the converter and vibrates the converter. However, the weight that is heavier than the speaker unit and is fixed to the rear side of the converter serves as a virtual ground and hence suppresses the vibration of the converter. Since the vibration of the converter is suppressed, even if the front portion of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be decreased and the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
In this speaker apparatus, mechanical vibration produced from an electrical signal by the converter is emitted, as sound waves, from the vibration plate to the neighboring air. Reactive force that acts on the vibration plate from the air is returned to the converter and vibrates the converter. However, the weight that is heavier than the speaker unit and is fixed to the rear side of the converter serves as a virtual ground and hence suppresses the vibration of the converter. Since the vibration of the converter is suppressed, even if the front portion of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be decreased and the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
Since the tip of the boss projecting from the weight is attached to the rear side of the external magnet type magnetic circuit in such a manner that the boss extends along the axial line of the voice coil, the area of junction between the magnetic circuit and the weight can be made small. As the junction area becomes larger, it becomes more difficult to join the weight to the rear side of the magnetic circuit uniformly over the entire junction surface and hence abnormal sound becomes more prone to occur due to vibration-induced closing and opening of a slight gap. However, in this speaker apparatus, since only the tip of the boss projecting from the weight is joined to the rear side of the magnetic circuit, sufficient junction uniformity can easily be secured. Where the weight is made of a ferromagnetic material such as iron, there is fear that magnetic flux may escape from the magnetic gap. However, in this speaker apparatus, since the weight is joined to the magnetic circuit only in the neighborhood of the axial line, even if the weight is made of a ferromagnetic material, its influence on the magnetic flux generated by the magnetic circuit can be minimized.
Since the tip of the boss projecting from the weight is attached to the rear side of the external magnet type magnetic circuit in such a manner that the boss extends along the axial line of the voice coil, the area of junction between the magnetic circuit and the weight can be made small. Since only the tip of the boss projecting from the weight is joined to the rear side of the magnetic circuit, sufficient junction uniformity can easily be secured. Further, since the weight is joined to the magnetic circuit only in the neighborhood of the axial line, even if the weight is made of a ferromagnetic material, its influence on the magnetic flux generated by the magnetic circuit can be minimized, whereby the electro-acoustic conversion efficiency of the speaker apparatus can be prevented from being reduced.
The magnetic circuit may be of an external magnet type and have an annular cancellation permanent magnet for decreasing leakage magnetic flux on the rear side of an annular main permanent magnet for generating magnetic flux for driving the voice coil. The boss of the weight may penetrate through a hollow portion of the cancellation permanent magnet and be fixed to the rear side of a center pole of the magnetic circuit.
With this configuration, although the cancellation permanent magnet for decreasing leakage magnetic flux is provided on the rear side of the magnetic circuit, since the boss of the weight can be joined to the magnetic circuit at a position close to the rear side of the main permanent magnet while penetrating through the hollow portion of the annular cancellation permanent magnet, vibration of the magnetic circuit can be suppressed by directly adding a weight to the magnetic circuit that receives reactive force from the voice coil.
Although the cancellation permanent magnet for decreasing leakage magnetic flux is provided on the rear side of the magnetic circuit, this configuration makes it possible to suppress vibration of the magnetic circuit by directly adding a weight to the magnetic circuit that receives reactive force from the voice coil.
A second aspect of the invention provides a speaker apparatus comprising a speaker unit including a main converter for converting an electrical signal into mechanical vibration, a vibration plate for emitting sound waves to the front side of the main converter, and a frame fixed to the converter, for vibratably supporting the vibration plate from a rear side thereof; a compensation converter for converting an electrical signal to mechanical vibration, the compensation converter being fixed to a rear side of the main converter and smaller and lighter than the main converter; and a compensation mass body lighter than the vibration plate, for serving as a load of mechanical vibration of the compensation converter.
With this configuration, the compensation converter that is smaller and lighter than the converter of the speaker unit is fixed to the rear side of the speaker unit, and the compensation mass body that is lighter than the vibration system of the speaker unit serves as a load of mechanical vibration of the compensation converter. The compensation converter is electrically driven so that the compensation mass body is given approximately the same momentum as the vibration system of the speaker unit is given when the converter of the speaker unit is driven, whereby the reactive force received by the converter of the speaker unit is made opposite in direction to that receivedby the compensation converter and the two reactive forces cancel out each other, as a result of which vibration can be suppressed. Since the vibration of the converters is suppressed, even if the front side of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
With this configuration, the compensation converter that is smaller and lighter than the converter of the speaker unit is fixed to the rear side of the speaker unit, and the compensation mass body that is lighter than the vibration system of the speaker unit serves as a load of mechanical vibration of the compensation converter. However, since the compensation converter is electrically driven so that the compensation mass body is given approximately the same momentum as the vibration system of the speaker unit is given when the converter of the speaker unit is driven, the reactive force received by the converter of the speaker unit is made opposite in direction to that received by the compensation converter and the two reactive forces cancel out each other, as a result of which vibration can be suppressed. Since the vibration of the converters is suppressed, even if the front side of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained. Since the compensation converter and the compensation mass body are made smaller and lighter, the weight of the speaker apparatus is not much increased.
A third aspect of the invention provides an acoustic signal output apparatus comprising a speaker unit including a main converter for converting an electrical signal into mechanical vibration, the main converter having a first movable portion capable of moving along a predetermined axial line, a vibration plate attached to the first movable portion, for emitting sound waves to a front side of the main converter, and a frame fixed to the main converter, for vibratably supporting the vibration plate from the rear side thereof; a compensation converter for converting an electrical signal to mechanical vibration, the compensation converter being fixed to a rear side of the main converter and having a second movable portion capable of moving along the predetermined axial line; a compensation mass body attached to the second movable portion, for serving as a load of mechanical vibration of the compensation converter; a signal source for generating an electrical signal corresponding to an acoustic signal to be outputted; and a signal processing circuit for receiving an output of the signal source, amplifying or attenuating the output, and supplying the main converter and the compensation converter with respective electrical signals having such phases that the first movable portion and the second movable portion move in opposite directions.
With this configuration, an electrical signal that is outputted from the signal source is supplied to the main converter and the compensation converter via the signal processing circuit, whereby the vibration plate of the speaker unit is driven and an acoustic signal is outputted. The main converter and the compensation converter are supplied with such electrical signals that the first movable portion and the second movable portion move in opposite directions. Therefore, reactive force received by the main converter and that received by the compensation converter have the same phase and act in opposite directions and hence cancel out each other, whereby vibration can be suppressed. This prevents adverse effects on an output acoustic signal and hence prevents deterioration in sound quality.
The signal processing circuit may comprise a first amplification circuit for amplifying a signal to be supplied to the main converter and a second amplification circuit for amplifying a signal to be supplied to the compensation converter, amplification factors of the first and second amplification circuits being determined in accordance with loads of mechanical vibration of the main converter and the compensation converter, respectively.
With this configuration, an electrical signal that is outputted from the signal source is amplified by the first amplification circuit and then supplied to the main converter, and is also amplified by the second amplification circuit and then supplied to the compensation converter. The amplification factors of the first and second amplification circuits are determined in accordance with the loads of mechanical vibration of the main converter and the compensation converter, respectively. For example, if the loads are the same, the amplification factors are set at the same value. If the loads are different from each other, the amplification factor of one amplification circuit corresponding to a converter having a smaller load is set larger than that of the other amplification circuit. With this configuration, even if the loads of the main converter and the compensation converter are different from each other, the two converters amplification factors of the drive currents, that is, electrical signals applied to the two converters, can be set correctly in accordance with, for example, a similarity ratio between the two converters.
The signal processing circuit may comprise an amplification circuit for amplifying a signal to be supplied to the main converter and the compensation circuit and an attenuation circuit for attenuating an output of the amplification circuit and supplying an attenuated signal to the main converter, an attenuation factor of the attenuation circuit being determined in accordance with loads of mechanical vibration of the main converter and the compensation converter.
With this configuration, an electrical signal that is outputted from the signal source is amplified by the amplification circuit. An output of the amplification circuit is on one hand supplied to the compensation converter as it is, and on the other hand attenuated by the attenuation circuit and then supplied to the main converter. The attenuation factor of the attenuation circuit is determined in accordance with the loads of mechanical vibration of the main converter and the compensation converter. With this configuration, With this configuration, the two converters amplification factors of the drive currents, that is, electrical signals applied to the two converters, can be set correctly in accordance with, for example, a similarity ratio between the two converters.
The invention further provides a speaker apparatus which converts an electrical signal into an acoustic signal and emits the acoustic signal to the front side, comprising a speaker unit including a converter for converting an electrical signal into mechanical vibration, a vibration plate provided on the front side of the converter, for emitting sound waves, and a frame fixed to the converter, for vibratably supporting the vibration plate from the rear side; a compensation converter fixed to a rear side of the converter of the speaker unit, for converting an electrical signal to mechanical vibration in the same manner as the converter of the speaker unit does; and a compensation vibrator for serving as a load of mechanical vibration of the compensation converter, the compensation vibrator being approximately as heavy as a vibration system of the speaker unit.
With this configuration, the compensation converter that is equivalent to the converter of the speaker unit is fixed to the rear side of the speaker unit, and the compensation vibrator approximately as heavy as the vibration system of the speaker unit serves as a load of mechanical vibration of the compensation converter. An electrical signal equivalent to an electrical signal for driving the converter of the speaker unit is applied to the compensation converter so that reactive force received by the converter of the speaker unit is opposite in direction to that received by the compensation converter, whereby the two reactive forces cancel out each other and vibration can be suppressed. Since the vibration of the converters is suppressed, even if the front side of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.
This configuration makes it possible to suppress vibration of the converters by generating, on the rear side of converter of the speaker unit, vibration that is equivalent to vibration occurring in the converter of the speaker unit and causing the two kinds of vibration to cancel out each other. Since the vibration of the converters is suppressed, even if the front side of the frame is fixed to an enclosure, vibration that is transmitted to the enclosure via the frame can be made small. Therefore, the emission of undesired sound from the enclosure can be suppressed, whereby sound quality with a good transient characteristic can be obtained.